Labiilit ikäykset ja stabiilit isotoopit : lisää ¹⁴C-ajoituksia Keminmaan Valmarinniemeltä
Ikäheimo, Janne (2018-06-07)
Ikäheimo, Janne (2018) Labiilit ikäykset ja stabiilit isotoopit : lisää ¹⁴C-ajoituksia Keminmaan Valmarinniemeltä. Faravid 45: 5-22.
© 2018 Janne Ikäheimo ja Pohjois-Suomen historiallinen yhdistys.
Labile datings and stable isotopes : more radiocarbon dates from the cemetery of Valmarinniemi
This follow-up article to a contribution published in Faravid 43 (2017: 107–128) examines and discusses eleven new radiocarbon dates — nine bone collagen dates from inhumation burials and two charred bone dates from cremation burials — obtained from the early Medieval cemetery of the Kemi parish, located at Cape Valmarinniemi in Keminmaa. The results (Table 1) were somewhat surprising, as they seem to challenge the chronology of the site based on the rate of post-glacial land-uplift, historical sources and the datable finds made during the excavations of the cemetery in 1981. The area of Valmarinniemi is estimated to have emerged from the sea during the 11th century, while the use of the cemetery is dated to the 14th and 15th centuries.
A partial explanation for "too old" dating results is the advanced decay of the unburned bone material recovered from the site. One of the samples (Beta-451048) sent to Beta Analytic Inc. for dating was contaminated with rootlets, while at least two bones from which samples were taken (Beta-451049 and Beta-451052) had been stabilized during conservation with Paraloid B-72 acrylic resin. While the radiocarbon service service provider treated both samples with a solvent to extract the resin, the anomalous dating result (Beta-451049) falling into the late first millennium AD indicates that the procedure had most likely been unsuccessful.
Reservoir effect is another factor to be taken into account when reviewing the dating results of inhumation burials, as the δ13C-values are somewhat elevated (−17.9–−21.0 ‰) probably reflecting the importance of marine resources, especially salmon and other fish, in the diet. Reservoir corrections were calculated with Calib 7.1 -online software using 262+100 years as a full reservoir effect correction and δ13Cmin −20.9 ‰ (terrestrial) and δ13Cmax −14.8 ‰ (marine) as threshold values (Figure 2). However, as the calculation of marine corrections did not have significant impact on the overall distribution of the results (Table 2), an explanation for their incompatibility with historical sources and coin data was sought from elsewhere.
One possibility worth considering is the contamination of the samples due to humic acids in the soil, which is hinted by the relative high C/N-ratio (3.7–4.0) in half of dated collagen samples and the high proportion of carbon (Cwt%) in them (Table 1 ). Hence, the most reliable dating results are probably the three bone collagen dates (Beta-451050, Beta-451055 and Beta-451056) and the two dates obtained from the charred bone of cremation burials E & K (Beta-451057 and Beta-451058). Together with six cremation burials radiocarbon dated in 2009, they can be used to deepen the picture about the site chronology.
While the deposition of cremated remains took place at the site from the 11th to the 14th century (Figure 1), this activity was at least partially synchronous with the practice of inhumation burials. On the other hand, the earliest burials of the "Christian" type in the cemetery date at the latest to the second half of the 13th century extending the overlap. The site chronology thus questions the relevance of long-cherished "pagan" vs. Christian dichotomy and supports recently expressed views stressing the resilience and hybridity often incorporated in relations and negotiations between different belief-systems. It is also likely that the cemetery includes an Orthodox Christian component as hinted by some artifacts found in the burials.
The stable isotope values measured from the samples alongside with their radiocarbon dates were juxtaposed with chronologically and chorologically comparable reference material consisting of both individuals as well as groups of people (Figure 3). While the population buried at Valmarinniemi were predictably eaters of C3-plants, the high δ¹⁵N-values point to the importance of marine fish in their diet. The values from the early modem period cemeteries of Kemi and Haukipudas are well aligned with the new results although the somewhat higher δ¹⁵N and slightly lower δ¹³C-values may point to the growing importance of agriculture in the area of coastal northem Ostrobothnia. This tendency was explored by plotting the new radiocarbon dating results against the δ¹⁵N- and δ¹³C-values measured from the same samples, and while both plots show uniform descendent tendency (Figure 4), the sample is simply not large enough to draw further conclusions about it. Finally, relating the location of the burial to the diet of the deceased produced a negative correlation. The person buried in the central part of the church (grave 141) had the lowest and the person buried well outside of it in the south (grave 123) the highest δ¹⁵N-value, hinting that the relation between the social status and the richness of the diet might not be as straightforward as often assumed.
The article is concluded with a suggestion for additional archaeological fieldwork to be carried out at Cape Valmarinniemi in the future. This would be necessary to obtain positively unaltered bone samples for additional radiocarbon dating, to georeference the 1981 excavation areas and to verify the state of preservation of those burials, which were discovered after the removal of the topsoil, but were not excavated down to the level of the burial.
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